The present invention relates to a computer and the like, and more particularly, to a computer and the like that has capability of reducing power consumption.
It is increasingly desirable from a standpoint of environmental issues today to reduce electrical power consumed during system power-off in a computer, especially, standby power when power is supplied by electrical power supply devices such as AC adapters. For example, a standard of Japan Environment Association (an incorporated foundation)'s Eco Mark (a trademark), established in the year 2000, stipulates that electrical power consumed during system power-off for a model including an AC adapter and no wakeup function should be 1W or less and that for a model with wakeup function be 5W or less. Wakeup function means a function to power on and start up a computer remote from a user, enabling a computer to be powered on with a direction from a network based on an operation at a remote place. A typical example of this function is WakeOnLAN, for example. The function allows powered-off computers to be managed in a centralized and collective manner.
In such a system, an active logic exists that consumes power at realization of wakeup function through communication even while the system is powered off. In case of WakeOnLAN, factors for this power consumption at wakeup include keeping a power supply VAUX ON for waking up a target Ethernet (a trademark) adapter so as to start up the PC upon recognizing a predetermined packet from a network. Due to such a factor, a system with wakeup function consumes more power during its power-off state than one without wakeup function.
Also, if an AC power supply exists in a system having a battery that can be used repeatedly through charging and discharging, a circuit required for battery charging function is always supplied with power even when the system is powered off (shut down). Such a circuit monitors battery state all the time for charging the battery, and consistently consumes about 100W if an AC power supply exists.
As a prior art relevant to reduction of power consumption, a technology exists that determines if charge of a backup capacitor is complete or not, and if complete, shuts off the power supply channel from the AC power supply in a power supply circuit having a backup capacitor for accumulating charging power (see, for example, Japanese Published Unexamined Patent Application No. 2000-4547 (pp3-4, FIG. 1).
In recent years, reduction of standby power for electrical products typified by computers especially has growing significance. As such, users who do not use functions relating to standby such as wakeup function also want to reduce standby power that is consumed during a state in which those functions relating to standby are enabled. However, modern systems do not provide interfaces for turning off charging function, for example. Additionally, a system which can be woken up is typically used with its wakeup function turned on, and reliable halt of the function requires complicated settings, thus limiting halt operation by a user.
On the other hand, although the technology disclosed in the Japanese Application mentioned above can indeed reduce power consumption during standby state when charging is not necessary, it just switches between connection and shut off of the AC power supply channel (primary) to a transformer within a device that internally includes a power supply. The technology thus cannot be applied to a device such as a notebook personal computer that does not internally include a power supply and has an external AC adapter for AC/DC conversion. Also, the technology does not control on/off of the function itself that is responsible for standby. As a result, while power consumption can be reduced when charging is not necessary, total power used for standby that is supplied by the capacitor remains the same, thus adversely more power is required when charging the capacitor, providing no reduction of overall power consumption.